Over the last few decades, the electronics industry has undergone a revolution through the use of semiconductor technology to fabricate small, highly integrated electronic devices. The most common semiconductor technology presently used is silicon-based. A large variety of semiconductor devices have been manufactured for various applications in numerous disciplines. Such silicon-based semiconductor devices include metal-oxide-semiconductor (MOS) transistors, complimentary MOS (CMOS) transistors, bipolar transistors, bipolar CMOS (BiCMOS) transistors, etc.
Each of these semiconductor devices generally includes a semiconductor substrate on which a number of active devices are formed. The particular structure of a given active device can vary between device types. For example, in MOS transistors, an active device generally includes source and drain regions and a gate electrode which modulates current between the source and drain regions. In bipolar transistors, an active device generally includes a base, a collector, and an emitter.
Many semiconductor devices have multiple layers of material that are deposited over a substrate to form one or more portions of the device (e.g., the gate electrode in a MOS device), as well as conducting lines and vias to connect devices and dielectric layers to isolate portions of the device and prevent unwanted connections. These layers can be deposited by a variety of techniques including chemical vapor deposition (CVD), sputtering, and evaporation.
Dielectric layers form barriers to isolate the other layers of the semiconductor device. Oxide materials are commonly used in semiconductor devices to form these dielectric barriers. For example, an oxide layer may separate a gate electrode from a substrate and adjacent active regions in a MOS semiconductor device or an oxide layer may fill a trench in devices that utilize trench isolation techniques to separate active regions in a substrate. Oxide layers may also isolate metal conductive lines. These oxide layers are often made of silicon dioxide, but other dielectric materials are commonly used for the same purposes.
Thin oxide layers, typically less than a few hundred angstroms, may be formed by thermal oxidation of the silicon substrate. To form thicker oxide layers or other oxide layers that can not be formed by thermal oxidation, chemical vapor deposition (CVD) is typically used. CVD typically involves reacting at least two gaseous materials to form a solid oxide. One method for forming silicon dioxide layers includes reacting tetraethyl orthosilicate (TEOS) with oxygen at about 400.degree. C. using well-known techniques such as Plasma Enhanced Chemical Vapor Deposition (PECVD).
Uniformity in deposition thickness between semiconductor wafers is a highly desirable property. Such uniformity often simplifies subsequent processing steps. However, the thickness of CVD layers can vary widely among devices prepared under similar conditions. This variation can create a corresponding variability in device parameters, which is typically undesirable. Thus, there is a need for methods of improving control and uniformity of deposition layer thickness.